1. Field of the Invention
The present invention relates to a valve device for use in a silencer that is interposed mainly in an exhaust system for a vehicle engine, and more particularly to a valve device which opens a bypass passage for exhaust gas in the silencer when the exhaust gas pressure rises to a certain pressure.
2. Discussion of Background Art
In general, a vehicle is required to ensure a sufficient engine output at a high speed rotating range in order to improve the performance during acceleration or high speed driving. Also, a vehicle is required to reduce exhaust noise in order to ensure calmness during idling or low speed driving. In other words, a vehicle is required to ensure a sufficient engine output at a high speed rotating range and is required to reduce exhaust noise of the engine at least at a low speed rotating range.
It is known that sectional area of a passage that forms an exhaust system of a vehicle engine has a great influence on engine output and exhaust noise. That is, with increasing the sectional area of the passage, more sufficient engine output can be obtained due to decreased exhaust resistance, however, more exhaust noise occurs with this decreased exhaust resistance. On the contrary, with decreasing the sectional area of the passage, less exhaust noise occurs due to increased exhaust resistance, however, the engine output decreases due to this increased exhaust resistance.
For this reason, Japanese Laid-open Patent Application No. 2001-123817 (see page 3 and FIG. 2, etc.) suggests to provide a bypass passage in the exhaust passage of a silencer that is provided in the exhaust system of the engine. The bypass passage further includes a valve device so that the bypass passage opens only during while driving at a high speed rotating range.
The valve device mainly includes a housing (base) having a valve opening, and a plate-like valve arranged to cover this valve opening. The plate-like valve is fixed to the housing at the proximal end thereof. The plate-like valve is deflected in accordance with pressure in the exhaust passage of the silencer and opens the valve opening.
However, exhaust gas pressure of the engine pulsates and the plate-like valve vibrates in accordance with the pulsation. Such vibration becomes greater at the distal end, and when the open/close vibration frequency conforms with the natural frequency of the plate-like valve, the plate-like valve resonates. When resonance of the plate-like valve occurs, operation of the valve disadvantageously becomes unstable or unusual noise occurs.
In view of the above, the present invention seeks to provide a valve device for a silencer, which restricts resonance of the plate-like valve.